Fix Air cache test dirty release state

[qasim-nylas]

Summary

• Prevent unbacked Air cache settings from resolving their base path to the package working directory.
• Keep Air cache-runtime test settings on the same temp directory as the test SQLite manager.
• Add regressions covering the empty settings base path and the cache test helper path.

Test Plan

• go test ./... -short
• git ls-files --others --exclude-standard internal/air